1. Field of the Invention
This invention relates generally to a flash fire control system for a photographic apparatus and, more particularly, to a flash fire control system for a photographic camera apparatus for providing a full range proportional fill flash over a broad range of camera-to-subject distances in ambient scene light intensity levels.
2. Description of the Prior Art
In the photographic art, exposure control systems embodying scanning shutter blade elements which operate to vary exposure areas with time during the exposure interval are well known as indicated by U.S. Pat. No. 3,942,183, entitled "Camera with Pivoting Blades", by G. Whiteside, issued Mar. 2, 1976, in common assignment herewith. Such scanning shutter blade mechanisms generally include a pair of counter-reciprocating shutter blade elements each having a primary aperture that traverses the optical axis of the camera during the exposure interval. The primary apertures are shaped so that upon overlying one another during countermovement of the blades, there is defined an effective exposure aperture value which increases to a maximum value in a determinate period of time.
Exposure control is provided by a pair of secondary photocell apertures in respective shutter blade elements which admit scene light to a photoresponsive element in correspondence with the scene light admitted to the focal plane during the shutter blade movement through an exposure cycle. The output from the photoresponsive element is directed to an integrator circuit which triggers upon reaching an integration level corresponding to a desired exposure value to terminate the exposure interval by returning the shutter blade elements back to their initial scene light blocking position.
Shutter mechanism of the aforementioned type are often arranged to operate in synchronism with a source of artificial illumination such as an electronic flash or strobe. The shutter blade mechanism and strobe are generally arranged to operate in either a high ambient scene light intensity mode of operation where no artificial illumination is provided or a low ambient scene light intensity mode of operation where the strobe is fired to provide a source of artificial illumination. Under conditions of low ambient scene light intensity where the strobe is expected to be fired, the scanning shutter blade mechanism may be stopped at an aperture value corresponding to the camera-to-subject distance as determined by focusing the objective lens. Systems of the aforementioned type are generally referred to as "follow focus" systems and the maximum aperture to which the scanning shutter blade elements are allowed to open is controlled by the rangefinding or focusing system in the camera in a manner as is more fully disclosed in U.S. Pat. No. 3,977,014, entitled "Follow Focus Exposure Control System with Improved Uniform Trim Control", by P. Norris, issued Aug. 24, 1976, in common assignment herewith.
Such a system need not actually stop the opening shutter blade movement at a maximum effective exposure aperture as determined by the rangefinding or focusing system of the camera but may, instead, vary the time at which the strobe light is fired during the opening shutter blade movement as determined in correspondence with the rangefinding or focusing system of the camera. Since the duration of the strobe light is short in comparison to the time required for the shutter blade mechanism to scan from its scene light blocking position to its maximum exposure aperture defining position, the aperture defined by the shutter blade elements at the instant of strobe firing for practical purposes constitutes the effective aperture by which the exposure occurs. Such a system is more fully described in U.S. Pat. No. 3,478,660, entitled "Photographic Apparatus with Flash Exposure Control System", by E. Land, issued Nov. 18, 1979, in common assignment herewith. Range responsive flash fire systems of the aforementioned type can also be utilized in conjunction with sonar rangefinding devices as more fully described in U.S. Pat. No. 4,188,103, entitled "Range Synchronized Flash Photographic Apparatus and Method for Achieving Optimum Exposure", issued Feb. 12, 1981, in common assignment herewith.
Exposure and artificial illumination control systems of the aforementioned type are generally intended to provide a source of artificial illumination only during the low ambient scene light intensity mode of operation. However, there may also be conditions during high ambient scene light intensity modes of operation where it becomes desirable to provide artificial illumination to fill in the photographic subject against a brightly back-lit scene as is more fully disclosed in U.S. Pat. No. 4,023,187, entitled "Exposure Control System with Fill Flash Race Condition", by E. Shenk, issued May 10, 1977, in common assignment herewith. The aforementioned artificial illumination control system operates under conditions of low ambient scene light intensity to fire the strobe at a predetermined time period subsequent to the initiation of the exposure interval and under conditions of high ambient scene light intensity to fire the strobe light as a consequence of the time integration of the scene light intensity incident to the photoresponsive element reaching a predetermined value. This fill flash system, however, fails to provide a select ratio between that portion of the exposure which is directly attributable to the artificial scene illumination and the remaining portion of the exposure which is directly attributable to ambient scene light illumination over a determinate range of camera-to-subject distances.
More recently, a photographic exposure and flash fire control system as disclosed in U.S. Pat. No. 4,192,587, entitled "Proportional Fill Flash", by A. LaRocque, issued Mar. 11, 1980, in common assignment herewith, is provided for firing of a strobe in a fill flash mode of operation in a manner whereby a select ratio may be maintained between that proportion of the exposure which is directly attributable to the artificial scene illumination and the remaining proportion of the exposure which is directly attributable to the ambient scene light illumination. Such a select proportional fill flash is accomplished by providing means whereby the light integration control circuit discounts the artificial illumination provided by the strobe. Toward this end, the system includes a sample and hold circuit which operates to sample the output voltage from a photoresponsive element and to transfer the sampled output voltage directly to a light integrating circuit. However, upon the firing of the strobe, the sample and hold circuit operates to hold the sampled voltage immediately prior to the firing of the strobe to apply the sampled voltage to the light integrating circuit for the duration of the strobe pulse.
For exposure control systems of the aforementioned type, it is often preferable to provide a substantially greater amount of artificial illumination during the ordinary flash mode of operation wherein the exposure influencing effect of the ambient scene light is negligible as opposed to the fill in flash situation where the ambient scene light contribution to the exposure is most significant. Toward this end, there may be provided a pre-exposure ambient scene light measurement, the results of which are utilized to subsequently control the amount of artificial illumination provided by the electronic flash or strobe during the exposure interval. Although ordinarily less artificial light might be provided during the fill in flash mode of operation, under certain circumstances such as increased ambient scene light intensity levels and greater camera-to-subject distances, it may become necessary to increase the amount of artificial illumination provided to maintain the same percentage contribution to exposure between the ambient scene light and the artificial scene light.
Therefore, it is a primary object of this invention to provide a flash fire control system wherein the output of the flash may be varied to maintain the same contribution to exposure between ambient and artificial scene light under conditions of increasing camera-to-subject distances and increasing levels of ambient scene light intensity.
It is a further object of this invention to provide a full range proportional fill flash control system for progressively increasing the amount of artificial illumination provided during the exposure interval in corresponding relationship with increasing levels of ambient scene light intensity and increasing camera-to-subject distances in order to maintain the same contribution to exposure between artificial and ambient scene light.
Other objects of the invention will be in part obvious and will in part appear hereinafter. The invention accordingly comprises a mechanism and system possessing a construction, combination of elements and arrangement of parts, which are exemplified in the following detailed disclosure.